Interpretive Summary: Five formulations containing different combinations of the active ingredients of DUETTM insecticide – prallethrin, sumithrin, and piperonyl butoxide (PBO) – were sprayed as ultra-low-volume (ULV) droplets in a wind tunnel. Female Culex quinquefasciatus Say mosquitoes exposed to sublethal amounts of spray were video recorded before, during, and after being sprayed. They were evaluated for movement and mortality, and the number and size of droplets on their bodies were later determined using a compound microscope. A positive correlation was discovered between mosquitoes that spent more time flying during the time of spraying and the number of droplets observed on their bodies. Excitation, in the form of increased speed and duration of flight, was immediate in mosquitoes exposed to prallethrin, whereas excitation in mosquitoes exposed to sumithrin occurred after spraying was terminated, and thus did not increase their exposure to the ULV droplets. The location of droplets on the bodies of mosquitoes, the effects of droplet volume, and mortality are also discussed.

Technical Abstract:
Mosquitoes are important in the United States due to their roles as pestiferous biters and vectors of diseases such as West Nile Virus and Dengue. Conventional applications of pesticides in spray clouds are often limited by their ability to contact and kill mosquitoes that may be resting or hiding in vegetation. A new commercial formulation for mosquito control, Duet™, contains a conventional active ingredient, sumithrin, in conjunction with a second pyrethroid insecticide, prallethrin. In this study conducted by scientists at USDA’s Center for Medical, Agricultural and Veterinary Entomology (CMAVE) in Gainesville (FL), prallethrin was examined for its role as an activator to increase exposure to pesticide and subsequent mortality of resting mosquitoes. Mosquitoes (Culex quinquefasciatus) exposed to prallethrin as droplets increased speed and duration of flight. More droplets were encountered by mosquitoes spending more time in flight resulting in higher mortality. These results suggest that products containing prallethrin can enhance mortality and thus efficacy of conventionally applied mosquito adulticides.